Field of the Invention
The invention relates to rolled products and structural elements made of aluminum alloy, particularly for aircraft construction.
Description of Related Art
While the competition between the materials for aeronautical construction intensifies, the commercial criteria in the selection of solutions are sometimes crucial. The manufacturer is primarily interested in the price per kilogram of materials in flight which corresponds to the product of the price per kilogram by the “buy to fly” ratio. The “buy to fly” ratio is the ratio between the raw material purchased by the aircraft manufacturer and the raw material mounted in the flying structure. The integral machining of aluminum parts from plates sometimes leads to a significant “buy to fly” ratio, notably for parts such as wing panels for which the required thickness is higher in the area of the wing root than at the wing tip. A plate is a rolled product having a rectangular cross-section of uniform thickness. For the fabrication of aeronautical structural elements, plates are currently used regardless of the final geometry of the part produced. Modification of the geometry of the plate, even if it is justified to save material has not yet been adopted by aircraft manufacturers as it presents disadvantages in terms of manufacturing, inspection and handling and because it does not allow for rapid transfer directly to the existing methods.
In addition, it is advantageous to produce monolithic metallic structural elements having variable properties in space so to obtain an optimum compromise of properties in each zone.
FR 2 707 092 describes a method for manufacturing structural age-hardened products, having continuously variable properties in at least one direction, in which aging is performed by bringing one end to temperature T and the other end to a temperature t in a special furnace comprising a hot chamber and a cold chamber connected through a heat pump.
WO 2005/098072 describes a method for manufacturing in which at least one step of the aging treatment is carried out in a furnace with a controlled thermal profile comprising at least two zones or groups of zones Z1 and Z2 with initial temperatures T1 and T2 in which the length of the two zones is at least one meter.
WO2007/122314 relates to a method for manufacturing a work-hardened product or a monolithic multi-functional structural element made of an aluminum alloy comprising a hot working step characterized in that after the hot working step, it also comprises at least one working step by cold plastic deformation in which different general deformations are imposed on at least two zones of the structural element, with a difference of at least 2% and preferably at least 3%. However, the methods described in this application are not implemented on an industrial scale.
Furthermore, US 2005/0279433 describes a method of flat-rolling a plate to obtain a variable thickness along its length, particularly suitable for aluminum or magnesium plates.
The problem addressed by this invention is to develop a method for manufacturing rolled products and monolithic structural elements made of aluminum alloy, notably for aircraft construction, having an improved “buy to fly” ratio and presenting compromises of optimized properties in each part.